Apparatus of the character to which the improvements according to the present invention find particular utility is disclosed in Pat. No. 4,587,796 to Haloila, the disclosure of which is hereby incorporated by reference herein for background purposes. This apparatus includes a stationary frame for receiving an article to be wrapped, a vertically reciprocable frame supported on the stationary frame, and a ring member supported on the reciprocating frame for displacement therewith and for rotation relative thereto about a vertical ring axis. A film carriage assembly is mounted on the ring member for displacement therewith, and a film clamping and sealing assembly is mounted on the reciprocable frame for displacement therewith, and these assemblies co-operate during rotation of the ring member to wrap the plastic film about the article and to heat seal the cut-off end thereof against the underlying wrap.
Heretofore, the support and drive arrangements for the ring member have necessitated that the latter be accurately formed or machined to a substantially perfect circular configuration, whereby construction of the ring member was extremely time consuming and expensive. Because of the required accuracy with respect to the roundness of the ring member, the latter was fabricated from two matching pieces suitably secured together and machined to obtain the necessary accuracy in profile. Further, if the ring member is driven by a belt and pulley arrangement as disclosed in the aforementioned Haloila patent, the time and expense is increased by providing the ring member with a belt groove and by providing a specially sized belt for the drive arrangement.
Further in connection with such wrapping apparatus heretofore available, guidance of the elevating and lowering of the reciprocable frame relative to the stationary frame assembly included complex guide roller arrangements between the stationary and reciprocable frame components. For example, the stationary frame was provided with vertical guide members having guide surfaces at 90.degree. to one another and the reciprocable frame was provided with guide rollers having roller axes at 90.degree. relative to one another for the rollers to engage the guide surfaces. The stationary and reciprocable frames are of rectangular configuration, and such guidance arrangements were provided at all four corners therebetween and had to be carefully adjusted relative thereto, thus adding to the time and expense of constructing the apparatus. Vertical guidance has also been provided by interengaging rollers and tracks at the four corners between the stationary and reciprocable frame units and in which the axes of the roller components at diametrically opposite corners of the apparatus are transverse to a line therebetween. Such guidance assemblies include specifically profiled rollers and tracks as well as adjustable roller units. Accordingly, these guidance arrangements are also undesirably expensive.
Another disadvantage in conjunction with wrapping apparatus of the foregoing character heretofore provided resides in the drive arrangement for elevating and lowering the reciprocable frame relative to the stationary frame structure. In this respect, the reciprocating drive was achieved by vertically extending chain drive units adjacent the four corners between the two frames. The chain units must be driven in unison to achieve elevation and lowering of the reciprocable frame without interference with the stationary frame and, more importantly, to achieve and maintain a horizontal disposition of the ring member and vertical disposition of the ring axis relative to the article being wrapped. Such unison in operation is extremely difficult to obtain and maintain due to the free play between chain and sprocket wheels which is compounded by a long endless chain belt in each of the four corners and the cross belts necessary for the four chains to be driven simultaneously. Moreover, the provision of five or six endless chain belts requires a considerable amount of link chain which adds to the cost of construction of the apparatus. Other arrangements have included link chains adjacent the four corners of the stationary and reciprocable frame units with one end of the chain attached to the reciprocable frame and the other end attached to a counterweight. The link chains extend around sprocket wheels on tile stationary frame, and the chains on opposite sides of the apparatus are driven in unison by an endless chain between the shafts supporting the sprocket wheels. Such an arrangement is also undesirably expensive with respect both to the provision of counterweights and appropriate support and guidance for the movement thereof during raising and lowering of the reciprocable frame.